Method For The Production Of A Support Web That Is Made Of Plastic With A Modified Mfi

ABSTRACT

The invention relates to a method for producing a support web ( 10 ) that is made of a predefined amount of plastic material by means of a plurality of molding elements ( 16, 17 ) which are formed in hollow spaces ( 12 ) of a mold ( 5 ), the plastic material being fed to the mold ( 5 ) via at least one extruder nozzle ( 1 ) of an extruder apparatus ( 18 ). In order to be able to lower the processing temperature while the plastic material obtains a very good molding behavior into the respective hollow spaces of a mold, the plastic material is intrinsically provided with at least one additive in such a way that the melt flow index (MFI) of the plastic material remains constant or preferably increases.

The invention relates to a method for the production of a support webthat is made of a definable amount of plastic material with a pluralityof molded elements which are shaped in the mold cavities of a moldingtool, the plastic material being supplied to the molding tool via atleast one extruder nozzle of an extruder means.

WO 02/13647 A2 discloses a process for producing a hook and loopfastener part, with a plurality of molded elements which are madesymmetrically and connected integrally to a support web, in the form ofinterlocking means in the form of a stalk provided with a head part, inwhich a moldable material is supplied to the shaping zone between apressure tool and a molding tool. In the known process, viewed at leastin a longitudinal section of the respective mold cavity the opposingboundary walls run continuously convexly, a continuously runningtransition between the cross sectional shapes of the stalk and head partfor an interlocking means of the support being achieved, so that anunimpeded mold removal process results.

In this process a suitable plastic granulate is plasticized via anextruder means and is supplied to the extruder nozzle of the extrudermeans for delivery to the molding tool. The plastic material used forthis purpose generally leads to colorless hook and loop fastener partswhich are of limited transparency. If the finished hook and loopfastener product is to be colored, it is possible to order the plasticgranulate used already colored and in this way supply it to the productprocess (master batch) or to add color pigments, for example in the formof titanium oxide, to the plastic granulate, for coloring white, and inthis way to supply it to the production process. Since the dyes used forthis purpose in addition to dye pigments of their chemical andmechanical behavior are not exactly known to the custom molder, and aredictated by the manufacturer, in the actual course of the productionprocess problems may arise, especially with respect to removing theindividual finished molded elements from the mold cavities of themolding tool.

Thus it has been found that when white dyes in the form of titaniumdioxide color pigments are added, the melt flow index (MFI) measured ingrams per 10 minutes for the plastic material clearly deteriorates, withthe result that this coloring process cannot be used at all in masterbatch operation for so-called micro-hook and loop fasteners, because, inthis way, due to the very poor flow behavior of the plastic, it can nolonger be delivered into the exceptionally geometrically small cavities(mold cavities) of the molding tool. Attempts undertaken in practice toimprove the molding behavior such that the molding temperature for theplasticized plastic material is increased however generally lead totemperature ranges being reached which damage the plastic material andmake production of hook and loop fastener products in the outlined rangeof sizes impossible. It is also difficult, without major cleaning efforton the extruder means to switch from one color to the next for thefinished hook and loop fastener product during the production processwhich proceeds more or less continuously.

To remedy this, the prior art (JP 07213310 A, JP 02283305 A and WO00/73063 A1) has already suggested coloring or/or printing of maleand/or female engagement parts of pressure sensitive adhesive fastenersby means of so-called inkjet or electrostatic application processes;however, on the one hand, extensive freedom of shaping in colorapplication in these processes also is not possible and on the other,these processes can only be economically carried out when large amountsof fastener material to be produced are colored with a dye. Theseprocesses are in turn limited in their application, if so-calledmicro-hook and loop fasteners are to be tinted in this way.

U.S. Pat. No. 6,136,046 A furthermore discloses, as so-called inkjet dyeapplication processes, in addition to electrostatically acting systemsand ultrasonic systems, also using piezoresistive element systems fordye application; but these processes also have application limits ifhook and loop fasteners are to be tinted with them, since the projectinghead parts on the ends of the fastener stalks form undercuts with themwhich can only be covered with difficulty by dye application from theoutside. If, as is recognized, the color is also applied only to the topof the hook and loop fastener material, it fundamentally wears, whichleads to decoloration of the fastener product over the long term.Conditions are comparable when the fastener material is printed with dyeor the dye is doctored onto the fastener material. Stria formation oftenoccurs unintentionally, as do problems in drying of the dye; this leadsto loss of quality. To be able to ensure reliable adhesion of the dye atall, “priming” and/or additional surface treatment processes arenecessary.

On the basis of this prior art, the object of the invention is to makeavailable a process for producing a hook and loop fastener product whichallows improved molding behavior of the plastic material into thecavities of a molding tool, with preferably simultaneous reduction ofthe processing temperature. Another object is to enable coloring for thehook and loop fastener product with such a process. These objects areachieved in principle by a process with the features of claim 1 in itsentirety.

In that, as specified in the characterizing part of claim 1, the plasticmaterial is intrinsically provided with at least one additive such thatthe melt flow index (MFI) of the plastic remains constant, preferablyrises, on the one hand the processing temperature can be reduced andstill very good molding behavior of the plastic material into therespective cavities of a molding tool is achieved. In particular, aprocessing temperature can be stipulated which does not damage theplastic material, and by increasing the melt flow index by way of therespective additive, improved molding behavior of the molded element ofthe hook and loop fastener product is achieved, so that so-called micro-or nano-hook and loop fasteners with the size of mold elements in themicro or nano range can be produced, especially with complicated moldgeometries (pronounced undercuts), as cannot be easily produced to datewith conventional processes.

Depending on the selected additive and as the melt flow index increases,other possibilities for influencing the hook and loop fastener productcan arise, such as for example adjusting the mechanical characteristicsof flexibility and toughness, by the additive causing an analogouschange of the crystallite formation in the plastic material during theshaping process.

Preferably a type of lubricant phase as the additive is supplied to theplastic material as another phase, the lubricant phase improving themolding behavior of the plastic material into the cavities of themolding tool with simultaneously reduced molding temperature. Thelubricant phase can be additives such as fatty acid esters, fatty acidester ethoxylates, paraffin oils, vegetable oils, such as biodegradablerapeseed oil or combinations thereof. This lubricant phase also ensuresthat even at elevated processing temperatures a reliable processsequence is ensured; this would not be guaranteed for example when usingsolvent-containing additives with respect to their combustibility (lowignition points).

It has been found to be especially advantageous to supply as anotheradditive a dye phase which forms a coloring liquid with the lubricantphase. Processing conditions are especially good when relative to theadded plastic material the proportion of the total additive isapproximately 0.05 to 5% by weight, preferably 0.2 to 0.6% by weight,especially preferably 0.5% by weight. It has also been found to beespecially favorable to use pigments with a particle size <10 μm to keepconstant or raise the melt flow index value as a dye for the dye phasein the indicated framework of percentages by weight. In this structurethen a fine dispersion of the pigment material is present in the plasticmatrix, especially in the form of a polymer matrix, with the result thatmigration processes for the colored particle portions of the suspensioncomposite which has been built up in this way are for the most partprecluded. It has also proven especially advantageous to use ultramarineblue as the dye for the dye phase in the indicated range of percentagesby weight to increase the melt flow index value.

If to increase the melt flow index the plastic material is intrinsicallyprovided with a coloring liquid by the coloring liquid being suppliedpreferably by a metering means from the outside to the extruder means ata location at which the plastic material is present at least partiallyplasticized, the initial material for the extruder means can beconventional plastic granulate which is known pertinently in terms ofits production behavior and can be managed in this way. If coloringliquid is supplied to the plasticized plastic material, it is thoroughlymixed with the coloring liquid from the inside (intrinsically) so thatthe degree of penetration for the entire plastic material is uniform.But it is also possible to supply the coloring liquid on the input sideto the extruder means to the latter without the plastic material havingto be plasticized until then.

Since the plastic material is tinted continuously and uniformly by meansof the coloring liquid supplied by way of the metering means, wearphenomena on the fastener material can be managed without this leadingto decoloration. Since the coloring liquid is supplied to the extrudermeans by way of the metering means, when the color is changed this canproceed promptly and especially without major cleaning efforts, so thata color change in a continuing production process leads only toextremely low scrap rates. Since a host of colors can be added as acoloring liquid, there are hardly any limits on the configurationpossibility and mixed colors for a hook and loop fastener part can beobtained in this way. Since color addition is very uniform, therequirements for increased product quality are likewise met.

Preferably the coloring liquids are those color systems as dye phaseswhich in addition to the actual dye and lubricant phase has binders andoptionally softeners, multivalent alcohols or amines as well as alcoholethoxylates. Since the lubricant phase of the coloring liquid is free ofsolvent, in this way at elevated processing temperatures within theextruder means safe dyeing operation can be achieved.

In one especially preferred embodiment of the process according to theinvention, depending on the plasticization state of the plastic materialand its temperature, a variable amount of the coloring liquid issupplied by the metering means such that a degree of tinting for thesupport web with the molded elements is made uniform. By way of thecorresponding sensors (temperature and pressure) the processingsituation of the plasticized plastic material within the extruder meanscan be reconstructed and by way of a suitable control means the meteringmeans is triggered such that for a compacted plastic material less coloris added and at reduced coherence a smaller amount of coloring liquid isadded. In this way uniform color addition to the plastic material ispossible and the finished product (hook and loop fastener product)produced later can be regarded as having been continuously uniformlycolored.

In another especially preferred embodiment of the process according tothe invention, the support web and/or the molded elements are coextrudedor produced from extrudable individual layers. In this multilayerstructure, if necessary each layer can be assigned its own color so thatthere is a host of shaping possibilities for coextruded fasteners.Preferably provision is made such here that in coextrusion for eachindividual layer there is its own extruder means in addition to theextruder nozzle and dye metering means. In this way, in thecorresponding replacement processes of the colors among the individuallayers the continuing production rates can be increased since withinproduction operation it is easily possible to change the color for eachpertinent individual layer.

Furthermore, it has been found to be especially favorable to supply thecoloring liquid within the extruder means by the metering means at thepoint at which the plastic material is supplied to the extruder nozzle.In this zone of the extruder means preferably a diamond-shaped mixer orthe like again homogenizes the compacted plastic material so that whenthe color is added at the homogenization site there, this leads tohomogenization of the color addition on the finished product (hook andloop fastener part). In addition or alternatively however it is alsopossible to supply the additive, especially in the form of a coloringliquid, at the start of the processing segment of the extruder means,for example by means of a metering hose pump.

The production process according to the invention is detailed belowusing one embodiment according to the single FIGURE. This FIGURE, whichis schematic and not to scale, shows a highly schematically simplifiedand partially cutaway side view of a device for carrying out the processaccording to the invention.

The FIGURE schematically shows parts of a device for executing theprocess according to the invention with an extruder head 1 as a supplymeans for especially thermoplastic material which is in the plastic orliquid state, which is supplied as a strip with a width whichcorresponds to that of the hook and loop fastener part to be produced,to a gap between a pressure tool 3 and a molding tool 5. The pressuretool 3 is a compression roll and the molding tool referred to as a wholeas 5 is a molding roll. Both rolls are driven in the directions ofrotation indicated with curved arrows 7 and 9 so that a conveyor gap isformed between them through which the plastic strip is conveyed in thetransport direction, while at the same time the material is molded intothe support strip 10 of the hook and loop fastener part and the supportstrip 10 on the side adjoining the molding roll acquires the shapenecessary to form the interlocking means (molded elements) by theshaping elements of the molding roll.

For this purpose the molding roll 5 on the periphery has a screen 11with individual mold cavities 12. Furthermore, the mold cavities 12,which are not detailed, are regularly distributed over the molding rollwith its screen 11 on the outer peripheral side, the distribution andnumber being freely selectable. In particular, the mold cavities 12 areprovided with boundary walls which run convexly so that a type ofhyperboloid structure is formed which corresponds to the molded elementto be produced. It is therefore possible with the indicated moldcavities 12 to produce interlocking means or molded elements in the formof one stalk part 17 provided with a head part 16. This productionstructure for interlocking means or other molded elements isconventional and is detailed for example in WO 02/13647 A2 so that itwill no longer be detailed here.

The plastic materials which are to be processed and which are being usedhere can be varied, for example in the form of polyamides orpolyolefins, such as polypropylene or polyethylene (HDPE, LDPE andLLDPE). Furthermore, other thermoplastics can also be used, such aspolyamides, polyesters (polyethylene terephthalate), polystyrenes,polycarbonates, polymethylmethacrylates, ethylene, vinyl acetatecopolymers including acrylate modified ethylenes, vinyl acetate polymersand ethylene acrylic acid copolymers and polyethylene styrenes.Furthermore there is use of thermoplastic elastomers such as naturallyor synthetically producible rubber including styrene block copolymerswith proportions of isoprene, butadiene or ethylene (butylene) blocks.Furthermore there is use for metallocene-catalyzed polyolefin,polyurethane or polydiorganosiloxanes. To stiffen the support web 10 andfor strengthening, ductile thermoplastics can be used, such as nylon orpolyvinyl chloride. The molded element articles produced in each case,especially in the form of a hook and loop fastener part, can also beprovided with coverings and coatings which can be vapor deposited ordoctored on. Furthermore, to produce structuring in the sense ofself-cleaning surfaces, post-treatments are possible, whether with alaser, ultrasound, or the like. In particular production materials canbe used which are biodegradable, as can those which can be especiallyeasily tinted.

For the purposes of the solution according to the invention, the plasticmaterial is provided intrinsically with at least one additive such thatthe melt flow index (MFI value) of the plastic material rises. This meltflow index value is generally measured in grams per 10 minutes. Innormal processing of thermoplastic material, for example in the form ofpolypropylene, with a sample density of 0.905 g/cm³ the average MFIvalues are approximately 61 g per 10 minutes. When an additive whichincreases the melt flow index value is introduced into the plasticmaterial, MFI values of an average of 71 are formed. This is equivalentto an increase of approximately 15%. To achieve this increase of the MFIvalue which can also be much higher, the additive is a type of lubricantphase which is supplied to the plasticized base material as anotherphase in order in this way to improve the molding behavior of theplastic material with simultaneously reduced molding temperature. Inthis way, so-called micro- or nano-hook and loop fasteners with moldedor interlocking elements on the order of magnitude of micrometers ornanometers can be easily produced.

Preferably the additive is a so-called coloring liquid which preferablyforms an apolar system and as the lubricant phase has liquid binders andthe actual dye. Furthermore, there can be so-called anticaking agents inthe coloring liquid as the system, and optionally other loadingmaterials, for example in the form of processing aids, stabilizers,antistatic agents, nucleation agents, etc. Binders or lubricants can befor example fatty acid esters and/or fatty acid ester ethoxylates,paraffin oils, including biodegradable oils, such as rapeseed oil. Useof biodegradable oils as the lubricant phase has the advantage that hookand loop fastener parts which have been produced in this way can also beused in critical fields, such as in the diaper or food sectors.Furthermore the coloring liquid can have softeners, multivalentalcohols, and/or amines and alcohol ethoxylates including other,system-specific components. They can be used either alone or in mixture.The choice of the lubricant phase depends preferably on thethermoplastic material to be tinted, or for elastomers, on the chemistryof the overall system. Very good values for increased MFI in any casehave been achieved when ultramarine blue is used as the dye for the dyephase.

In the thermoplastic materials preferably being used here, mainly fattyacid esters, fatty acid ethoxylates, paraffin oils and vegetable oils,and in the case of PVC, softeners have proven effective. To produce acoloring liquid the formulation components which have been weighed inare added to or dispersed into the pertinent agents and then ground.This grinding is not actual primary grain crushing, but simple breakingup the agglomerates as completely as possible in order to thus achieveoptimum dispersion of the dyes in the binder system.

The aforementioned extruder head 1 with the extruder nozzle is a part ofan extruder means referred to as a whole as 18. This extruder means 18has an extruder worm which is not detailed, and which extends from anentry zone 20 to the extruder head 1 with the extruder nozzle. Thisextruder worm is continuously driven via a drive, for example in theform of an electric motor 22. An entry point 24 for supply of theplastic granulate which is not detailed, for example in the form of athermoplastic material, is connected to the entry zone 20. Within theextruder means 18 a heating and compaction zone 26 is connected to theentry zone 20; the heating and compaction zone on its side facing awayfrom the entry zone 20 discharges into a homogenization zone 28 to whichthen in turn the extruder head 1 with the extruder nozzle is connected.The homogenization zone 28 is preferably formed by a diamond-shapedmixer (not shown) which is integrated into the extruder worm. Thehomogenization zone 28 is designed especially to re-homogenize possiblycompacted plastic material before the pertinent material is discharged.

A metering means referred to as a whole as 30 is connected to thehomogenization zone 28, this means being shown simplified in the FIGUREin the form of a black box. In addition to the control means 32, themetering means 30 still has at least one dye storage tank 34 for therespective coloring liquid. Furthermore, sensors for pressure p,temperature T and possibly the velocity v of the plastic material alsodischarge into the homogenization zone, the pertinent outputs of thesensors 36 being analogously connected to the inputs of the meteringmeans 30. In addition to the indicated sensors, still other sensors canbe used (not shown), for example for viscosity, etc. Preferably it isfurthermore provided that pressure sensors be located at various sitesto be able to determine the pressure differences in this way for theanalogous triggering of the metering means 30 to obtain uniform colordelivery into the plastic material.

The respective operating state of the plastic material in thehomogenization zone 28 is detected by means of the sensors 36, anddepending on this the control means 32 feeds the liquid dye stored inthe tank 34 into the homogenization zone 28 of the extruder means 18. Ifchanges on the plastic material occur due to the properties, forexample, it is compacted, less coloring liquid is supplied via themetering means 30 than if the plastic material were not too tightlypacked.

In this way, it is ensured by way of the metering means 30 that dyealways travels uniformly into the plastic material; for the finishedproduct this later leads to the dye being homogeneously addedcontinuously. Furthermore, the metering means 30 makes it possible toremove coloring liquid if necessary from several color storage tankswhich are not shown, to mix them and then to deliver them in mixed format the same time or in alternation into the plastic material. If thesupport web 10 is to be built up into several layers in the coextrusionprocess, each layer can be assigned its own extruder means, with its ownmetering means for the coloring liquid so that each layer fundamentallycould be assigned it own color. Since the path between thehomogenization zone 28 and the extruder head 1 is very short, for apossible color change an immediate changeover to the next color would bedirectly possible, and in this way the scrap rate for unwanted coloringor discolored material can be largely reduced. Another possibility foradding color also consists in supplying the coloring liquid at the inputof the extruder means 18 to the latter by means of a hose metering pumpwhich is not shown, for example at the entry site 24, in the region ofthe entry zone 20 or directly behind the entry zone 20.

If, as is shown in the prior art, in so-called master batch operationtitanium oxide as the coloring pigment is supplied to the plasticmaterial, for example in the form of a polypropylene material, the meltflow index MFI decreases in a duplicated comparison measurement to 46 gper 10 minutes; this results in that for the pertinent coloring processa much higher shaping temperature can be selected in order to be able toensure the molten molding behavior of the plastic material which isrequired for the cavities in a comparable production situation. But thelatter leads to high thermal loading of the plastic material; thisultimately indicates the limits for free shaping so that in this wayonly standard fasteners with relative large geometrical dimensions canbe colored. It is not possible to produce micro-hook and loop fastenersystems in this way. It has been shown that with the increase of themelt flow index values with respect to consideration of enthalpy alarger amount of heat can be permanently delivered into the plasticmaterial which in this way dictates improved shaping behavior, and it issurprising that by suitable selection of the additive free crystalformation in the plastic material can be controlled such that mechanicalcharacteristics such as flexibility and toughness can be dictated withina wide framework; this is not possible with the delivery systems knownto date (titanium oxide).

The process according to the invention is especially suited to producingso-called micro- or nano-hook and loop fasteners in which the individualinterlocking elements have a height and/or width which is between 0.05mm and 1 cm, especially in the value range from 0.6 mm to 1 mm. In thisway then there can be up to 500 interlocking means per square centimeterof the support web 10 which is to be produced. In one preferredembodiment of the solution according to the invention, up to 16,000 hookand loop elements and more on a square centimeter of support web 10 arepossible. Calculated from the top of the support web 10 to thetermination of the respective interlocking or hook and loop element overthe flat head top, each pertinent element has a height of approximately100 μm, the flat head tops having a diameter of approximately 50 μmwhich can be reduced in the direction toward the top end of the stalkpart 17 to a size of approximately 30 μm. For this purpose, between thehead part 16 and the stalk part 17 an undercut is formed at the site ofthe transition. The height of the head part 16 is approximately 10 μmand the size of the radial projection of the head part 16 to the top endof the stalk part 17 is also likewise approximately 10 μm. The distancesbetween the border of adjacently opposite head parts 16 are 30 μm to 40μm. The diameter of the stalk parts 17 is approximately 20 μm to 35 μm.These size conditions are only examples and can be altered in theindicated range of sizes. With the process according to the invention itis possible for the first time to continuously provide extremely smallor micro-hook and loop fasteners with a color; this is not possible withconventional means.

1. Method for the production of a support web (10), consisting of adefinable amount of plastic material, with a plurality of moldedelements (16, 17) which are shaped in the mold cavities (12) of amolding tool (5), the plastic material being supplied to the moldingtool (5) via at least one extruder nozzle (1) of an extruder means (18),characterized in that the plastic material is intrinsically providedwith at least one additive such that the melt flow index (MFI) of theplastic remains constant, preferably rises.
 2. The process according toclaim 1, wherein the respective additive as a type of lubricant phase issupplied to the plastic material as another phase, and wherein thelubricant phase improves the molding behavior of the plastic materialinto the cavities of the molding tool with preferably simultaneouslyreduced molding temperature.
 3. The process according to claim 2,wherein as another additive a dye phase which forms a coloring liquidwith the lubricant phase is supplied.
 4. The process according to claim3, wherein ultramarine blue is used as the dye for the dye phase.
 5. Theprocess according to claim 1, wherein relative to the added plasticmaterial the proportion of additive is approximately 0.05 to 5% byweight, preferably 0.2 to 0.6% by weight, especially preferably 0.5% byweight.
 6. The process according to claim 2, wherein additives such asfatty acid esters, fatty acid ester ethoxylates, paraffin oils,vegetable oils, such as biodegradable rapeseed oil or combinationsthereof are used as the lubricant phase.
 7. The process according toclaim 1, wherein the additive is provided with other components such assofteners, multivalent alcohols, amines as well as alcohol ethoxylates.8. The process according to claim 1, wherein the additive, especially asa coloring liquid, is supplied by a metering means (30) from the outsideto the extruder means (18) at a location at which the plastic materialis present at least partially plasticized.
 9. The process according toclaim 8, wherein depending on the plasticization state of the plasticmaterial and/or its temperature (T), a variable amount of the coloringliquid is supplied by the metering means (30) such that a degree oftinting for the support web (10) with the molded elements (16, 17) ismade uniform.
 10. The process according to claim 1, wherein theadditive, especially as a coloring liquid, is supplied at the input ofthe extruder means (18) by means of a hose metering pump which is notshown, for example at the entry site (24) for supply of a plasticgranulate, in the region of the entry zone (20) which is upstream of theextruder means (18) or directly behind the entry zone
 20. 11. Theprocess according to claim 1, wherein the support web (10) and/or themolded elements (16, 17) are coextruded or are composed of individuallayers which can be coextruded.
 12. The process according to claim 11,wherein for coextrusion for each individual layer there is its ownextruder means (18) with extruder nozzle (1) and color metering means(30).
 13. The process according to claim 1, wherein the coloring liquidwithin the extruder means (18) is supplied by the metering means (30) atthe point (homogenization zone (28) at which the plastic materialtravels into the extruder nozzle (1) and/or at a point which is adjacentto the one at which the plastic material is supplied to the extrudermeans (18).